Some internal combustion engines utilize a compression device such as a turbocharger to increase engine torque/power output density. In one example, a turbocharger may include a compressor connected to a turbine via a drive shaft, where the turbine is coupled to an exhaust manifold side and the compressor is coupled to an intake manifold side of an engine. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the pressure (e.g. boost or boost pressure) in the intake manifold and to increase the flow of air into the engine. The boost may be controlled by adjusting the amount of gas reaching the turbine, for example with a wastegate. A wastegate valve may be controlled based on operating conditions to achieve the desired boost. In some examples, the wastegate valve is actuated pneumatically, while in other examples the wastegate valve is actuated electrically, for example by an electric motor.
U.S. Pat. No. 7,775,043 discloses a system for controlling the boost pressure supplied to an internal combustion engine by adjusting the position of a wastegate valve in a pneumatic wastegate. A wastegate sensor positioned proximate the wastegate valve senses the position of the wastegate valve and delivers a signal representative of the position via a conductor to a controller. The controller receives a plurality of signals including indications of engine speed, boost, and barometric pressure to control the boost pressure supplied to the engine, and accordingly adjusts the position of the wastegate valve by controlling the pressure supplied to a chamber acting against a diaphragm of the wastegate. In the event it is determined that the wastegate valve is not functioning properly, the controller may use signals from the wastegate sensor to re-determine the position of the wastegate valve.
The inventors herein have recognized an issue with such an approach. Portions of the wastegate, such as the wastegate valve and linkage coupling the wastegate valve to the diaphragm (or other actuator in other systems such as an electric motor), encounter high temperatures as the engine heats up and hot exhaust gas is circulated throughout the engine. Due to the exposure of these components to high temperatures, thermal deformation may occur, causing, for example, elongation or contraction in the valve-actuator linkage, and turbine housing deformation. As such, the accuracy of wastegate valve position sensing decreases, as does the knowledge of the location of valve lift with respect to a seat which the wastegate valve contacts at a fully closed position. The degradation of such accuracy may result in the supply of inaccurate levels of boost to the engine.
Methods for determining the fully closed position of a wastegate valve are provided.
In one example, a non-closed position command for a wastegate valve in a low-lift region relative to a valve seat is received. Prior to executing the position command, the wastegate valve is only temporarily closed to thereby determine a fully closed position.
In this way, inaccurate boost supply due to indeterminacy of the fully closed position is avoided. Thus, the technical result of more accurate wastegate control is achieved by these actions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.